This application is a 371 of PCT/EP96/01088, which was filed on Mar. 14, 1996.
The present invention relates to cosmetic or dermatological gels based-on microemulsions, in particular such gels for cosmetic and dermatological formulations. As a particular embodiment, the present invention relates to cosmetic or dermatological gels based on microemulsions of the oil-in-water type, processes for their preparation and their use for cosmetic and medical purposes.
Cosmetic skin care is primarily to be understood as meaning that the natural function of the skin as a barrier against environmental influences (for example dirt, chemicals and microorganisms) and against the loss of endogenous substances (for example water, natural fats and electrolytes) is intensified or re-established.
If this function is impaired, increased absorption of toxic or allergenic substances or attack by microorganisms and as a consequence toxic or allergic skin reactions may occur.
The aim of skin care is furthermore to compensate the loss of fats and water from the skin caused by daily washing. This is important particularly if the natural capacity for regeneration is not adequate. Skin-care products should furthermore protect against environmental influences, in particular against the sun and wind, and delay ageing of the skin.
Medical topical compositions as a rule comprise one or more medicaments in an active concentration. For simplicity, reference is made to the legal provisions of the Federal Republic of Germany (for example cosmetics legislation, legislation on foodstuffs and medicaments) for a clear distinction between cosmetic and medical use and corresponding products.
Gels are customary cosmetic and dermatological formulation forms which have become more and more wide-spread particularly in recent times.
In the technical sense, gels are understood as meaning: relatively dimensionally stable, easily deformable disperse systems of at least two components, which as a rule comprise axe2x80x94usually solidxe2x80x94colloidally divided substance of long-chain molecular grouping (for example gelatin, silicic acid or polysaccharides) as the matrix-forming phase and a liquid dispersing agent (for example water). The colloidally divided substance is often called a thickener or gelling agent. It forms a three-dimensional network in the dispersing agent, it being possible for individual particles present in colloidal form to be linked to one another more or less firmly via electrostatic interaction. The dispersing agent, which surrounds the network, is distinguished by electrostatic affinity for the gelling agent, i.e. a predominantly polar (in particular: hydrophilic) gelling agent preferably gels a polar dispersing agent (in particular: water), whereas a predominantly non-polar gelling agent preferably gels non-polar dispersing agents.
Strong electrostatic interactions, which are realized, for example, in hydrogen bridge bonds between the gelling agent and dispersing agent, but also between dispersing agent molecules with one another, can lead to a high degree of crosslinking of the dispersing agent as well. Hydrogels can comprise water to the extent of almost 100% (alongside, for example, about 0.2-1.0% of a gelling agent), and at the same time have an entirely solid consistency. The water content is present here in ice-like structural elements, so that gels entirely justify the origin of their name [from lat. xe2x80x9cgelatumxe2x80x9d=xe2x80x9cfrozenxe2x80x9d by the alchemistic term xe2x80x9cgelatinaxe2x80x9d (16th century) for the modern term xe2x80x9cgelatinxe2x80x9d].
Lipogels and oleogels (of waxes, fats and fatty oils) as well as carbogels (from paraffin or petrolatum) are furthermore also customary in cosmetic and pharmaceutical galenics. In practice, a distinction is made between oleogels, which are in practically anhydrous form, and hydrogels, which are practically fat-free. Gels are usually transparent. In cosmetic and pharmaceutical galenics, gels are as a general rule distinguished by a semi-solid, often free-flowing consistency.
In simple emulsions, in the one phase, finely dispersed droplets of the second phase (water droplets in W/O or lipid vesicles in O/W emulsions) enclosed by an emulsifier shell are present. The droplet diameters of the usual emulsions are in the range from about 1 xcexcm to about 50 xcexcm. Without further colouring additives, such xe2x80x9cmacroemulsionsxe2x80x9d are milky white in colour and opaque. Finer xe2x80x9cmacroemulsionsxe2x80x9d, the droplet diameters of which are in the range from about 10xe2x88x921 xcexcm to about 1 xcexcm, again without colouring additives, are bluish-white in colour and non-transparent.
It is the property of micellar and molecular solutions having particle diameters of less than about 10xe2x88x922 xcexcm to appear clear and transparent.
The droplet diameter of transparent or translucent microemulsions, on the other hand, is in the range from about 10xe2x88x922 xcexcm to about 10xe2x88x921 xcexcm. Such microemulsions usually have a low viscosity. The viscosity of many microemulsions of the O/W type is comparable to that of water.
So-called surfactant gels are furthermore customary formulations of the prior art. These are understood as being systems which, in addition to water, have a high concentration of emulsifiers, typically more than about 25% by weight, based on the total composition. If oil components are solubilized in these surfactant gels, which is their technical name, microemulsion gels, which are also called xe2x80x9cringing gelsxe2x80x9d are obtained. Cosmetically more elegant microemulsion gels can be obtained by addition of nonionic emulsifiers, for example alkyl poly-glycosides. Here also, the high content of emulsifiers is a disadvantage.
An advantage of microemulsion gels is that active compounds can be present in finely disperse form in the disperse phase. Another advantage is that, because of their low viscosity, they can be sprayed. When microemulsions are used as cosmetics, corresponding products are distinguished by a high cosmetic elegance.
It is known per se to link the droplets of a low-viscosity, in particular thinly liquid microemulsion with crosslinking substances with one another, in order to obtain the three-dimensional network of a gel in this manner.
Chain-like, hydrophilic molecules which contain a hydrophobic radical on each of the two chain ends are described in Nachr. Chem. Techn. Lab. 43 (1995) No. 1, page 9 et seq for crosslinking microemulsion droplets. Those hydrophobic radicals are immersed in the microemulsion droplets, the hydrophilic chain regions being in the continuous aqueous phase. In the strict sense, it is certainly not necessary for the hydrophobic radicals to be xe2x80x9cimmersedxe2x80x9d. In individual cases, it can also be entirely sufficient if the hydrophobic radicals come into contact with. the surface of the microemulsion droplets by hydrophobic interaction and remain stuck to these more or less firmly.
Crosslinking agents which are mentioned in the above reference are polyoxyethylene glycols with oleyl groups as hydrophobic end groups.
This principle is illustrated in FIG. 5: the microemulsion droplets of an O/W microemulsion, which are shown as shaded circles, are joined to one another by the crosslinking agent molecules shown as lines, these carrying hydrophobic radicals, symbolized by rectangles, at both ends. It can be seen that in principle an emulsion droplet can also accommodate several hydrophobic radicals, as a result of which a higher degree of crosslinking and three-dimensionality of the network can be ensured.
A disadvantage of microemulsions, and therefore also of the microemulsion gels of the prior art, is that a high content of one or more emulsifiers must always be employed, since the low droplet size results in a high interface between the phases, which as a rule must be stabilized by emulsifiers.
The use of the customary cosmetic emulsifiers is indeed acceptable per se. Nevertheless, emulsifiers, like any chemical substance in the end, can cause allergic reactions or reactions based on hypersensitivity of the user in an individual case.
It is thus known that particular photodermatoses are induced by certain emulsifiers, and also by various fats, and simultaneously exposure to sunlight. Such photodermatoses are also called xe2x80x9cMajorca acnexe2x80x9d. An object of the present invention was therefore to develop sunscreen products.
As particular embodiments, the present invention thus relates to cosmetic and dermatological light protection formulations, in particular skin-care cosmetic and dermatological light protection formulations.
The damaging effect of the ultraviolet part of solar radiation on the skin is generally known. While rays having a wavelength of less than 290 nm (the so-called UVC range) are absorbed by the ozone layer in the Earth""s atmosphere, rays in the range between 290 nm and 320 nm, the so-called UVB range, cause erythema, simple sunburn or even actual burns of greater or lesser severity.
The narrower range around 308 nm is seen as the erythema activity maximum of sunlight.
Numerous compounds are known for protection against UVB radiation, these usually being derivatives of 3-benzylidenecamphor, of 4-aminobenzoic acid, of cinnamic acid, of salicylic acid, of benzophenone and also of 2-phenylbenzimidazole.
For the range between about 320 nm and about 400 nm, the so-called UVA range, it is also important to have available filter substances, since the rays thereof can also cause damage. It has thus been proved that UVA radiation leads to damage to the elastic and collagenic fibres of connective tissue, which makes the skin age prematurely, and that it has to be regarded as a cause of numerous phototoxic and photoallergic reactions. The damaging effect of UVB radiation can be intensified by UVA radiation.
However, UV radiation can also lead to photo-chemical reactions, the photochemical reaction products then intervening in the skin metabolism.
To prevent these reactions, antioxidants and/or agents which trap free radicals can additionally be incorporated into the cosmetic or dermatological formulations.
Most inorganic pigments, which are known to be used in cosmetics for protecting the skin against UV rays, are UV absorbers or UV reflectors. These pigments are oxides of titanium, zinc, iron, zirconium, silicon, manganese, aluminium and cerium, and mixtures thereof, as well as modifications.
Microemulsion gels are also suitable for other cosmetic dermatological uses, for example deodorants, so that in a particular embodiment, the present invention relates to microemulsion gels as a base for cosmetic deodorants.
Cosmetic deodorants serve to eliminate body odour, which develops when fresh perspiration, which is odourless per se, is decomposed by microorganisms. The customary cosmetic deodorants are based on various action principles.
In so-called antiperspirants, the formation of perspiration can be reduced by astringentsxe2x80x94chiefly aluminium salts, such as aluminium hydroxy chloride (hydrated aluminium chloride).
By using antimicrobial substances in cosmetic deodorants, the bacterial flora on the skin can be reduced. In the ideal case, only the odour-causing microorganisms should be effectively reduced here. The flow of perspiration itself is not influenced as a result, and in the ideal case only the microbial decomposition of the perspiration is temporarily stopped.
Combination of astringents with antimicrobially active substances in one and the same composition is also customary.
Deodorants should meet the following conditions:
1) They should cause reliable deodorization.
2) The natural biological processes of the skin must not be impaired by the deodorants.
3) The deodorants must be harmless in the event of an overdose or if used other than as specified.
4) They should not become concentrated on the skin after repeated use.
5) They should be easy to incorporate into customary cosmetic formulations.
Both liquid deodorants, for example aerosol sprays, roll-ons and the like, and solid formulations, for example deodorant sticks, powders, powder sprays, intimate cleansing compositions and the like, are known and customary.
The use of microemulsions as a base for formulations having a deodorizing or antiperspirant action is also known. Their relatively high content of emulsifiers with the disadvantages described has to date been a poor state of affairs which was to be remedied.
Another object of the present invention was thus to develop formulations which are suitable as a base for cosmetic deodorants or antiperspirants and do not have the disadvantages of the prior art.
It was furthermore an object of the invention to develop cosmetic bases for cosmetic deodorants which are distinguished by a good skin tolerability.
It was furthermore an object of the present invention to provide products based on microemulsion gels with the broadest possible diversity of uses. For example, bases for formulation forms such as cleansing emulsions, face- and body-care formulations, and also distinctly medical/pharmaceutical presentation forms, for example formulations against acne and other skin manifestations, were to be provided.
In a particular embodiment, the invention therefore relates to cleansing emulsions, in particular facial cleansing emulsions, preferably make-up removers, for example eye make-up removers.
Such formulations are known per se. They are usually mixtures of cosmetic oils or aqueous formulations of surface-active substances, the function of which is to solubilize the contamination or the make-up particles and remove them from the skin.
Waterproof eye make-up, for example mascara, can be removed satisfactorily with water-based make-up removers only with special surfactants. However, these surfactants often have only a limited physiological tolerability. When such substances come into contact with the mucous membrane, in particular the mucous membrane of the eye, these substances lead to irritation, which manifests itself, for example, in a reddening of the eyes. Reactions of this type are typical of surfactant-containing products.
An object of the present invention is consequently to provide a remedy for such problems.
In another embodiment, the present invention relates to hair cosmetics formulations. In particular, the present invention relates to hair cosmetics formulations for care of the hair and the scalp. In a preferred embodiment, the present invention relates to formulations which serve to strengthen the individual hairs and/or to impart hold and fullness to the hairstyle overall.
Roughly speaking, human hair can be divided into the living part, the hair root, and the dead part, the hair shaft. The hair shaft in turn comprises the medulla, which nevertheless through evolution has become insignificant for modern man and has receded, and in the case of thin hair is often absent entirely, and furthermore the cortex which surrounds the medulla and the cuticula which encloses the entirety of the medulla and cortex.
The cuticula in particular, but also the keratinous region between the cuticula and cortex, as the outer shell of the hair, are exposed to particular demands due to environmental influences, due to combing and brushing, and also due to hair treatment, in particular colouring of the hair and deforming of the hair, for example permanent wave processes.
When exposed to particularly aggressive demands, for example bleaching with oxidizing agents, such as hydrogen peroxide, in which the pigments distributed in the cortex are destroyed by oxidation, the inside of the hair can also be affected. If human hair is to be coloured permanently, in practice only oxidizing hair-colouring processes are possible. In the case of oxidative colouring of the hair, the dyestuff chromophores are formed by reaction of precursors (phenols, aminophenols and less frequently also diamines) and bases (usually p-phenylenediamine) with the oxidizing agent, usually hydrogen peroxide. Hydrogen peroxide concentrations of about 6% are usually used for this.
The process is usually based on a bleaching action by the hydrogen peroxide taking place, in addition to the colouring action. In human hair coloured by oxidation, as with bleached hair, microscopic holes are detectable at the points where melanin granules were present. It is a fact that the oxidizing agent hydrogen peroxide reacts not only with the colour precursors but also with the hair substance and as a result under certain circumstances can cause damage to the hair.
Washing the hair with aggressive surfactants can also make demands on the hair, and at least reduce its appearance or the appearance of the hairstyle overall. For example, certain water-soluble hair constituents (for example urea, uric acid, xanthine, keratin, glycogen, citric acid and lactic acid) can be leached out by washing the hair.
For these reasons, in some cases hair-care cosmetics which are intended to be rinsed out of the hair again after their action and in some cases those which are to remain on the hair have been used for a relatively long time. The latter can be formulated such that they not only care for the individual hair, but also improve the appearance of the hairstyle overall, for example by imparting to the hair more fullness, fixing the hairstyle over a longer period of time or improving its ease of styling.
For example, the combability of hair can be improved decisively by quaternary ammonium compounds. Such compounds are absorbed onto the hair and are often still detectable on the hair after the hair has been washed several times.
However, the prior art has lacked active compounds and formulations which satisfactorily provide care for damaged hair. Formulations which should give the hairstyle fullness have also often proved to be inadequate, or at least they were unsuitable for use as hair-care formulations. Formulations of the prior art which fix the hairstyle as a rule comprise, for example, viscous constituents, which run the risk of giving rise to a feeling of tackiness, which often has to be compensated by skilful formulation.
An object was therefore to remedy the disadvantages of the prior art.
A particular object of the present invention was to provide gelatinous formulations based on finely dispersed systems of the oil-in-water type with the lowest possible emulsifier content which do not have the dis-advantages of the prior art and which can have the most diverse cosmetic and/or dermatological applications, for example the uses described above. Another object of the invention was to enrich the limited range of gelatinous formulations based on finely dispersed systems of the oil-in-water type of the prior art.
It is known per se that hydrophilic emulsifiers, that is to say polyethoxylated and polypropoxylated emulsifiers, change their solubility properties from water-soluble to fat-soluble as the temperature increases. A characteristic of the hydrophilicity of a given emulsifier is its HLB value.
The definition of the HLB value for polyol fatty acid esters is given by the formula I
HLB=20*(1xe2x88x92S/A)
For a group of emulsifiers, the hydrophilic content of which comprises only ethylene oxide units, the formula II applies
HLB=E/5
wherein S=saponification number of the ester,
A=acid number of the acid recovered
E=proportion by weight of ethylene oxide (in %) in the total molecule.
Emulsifiers having HLB values of 6-8 are in general W/O emulsifiers, and those having HLB values of 8-18 are in general O/W emulsifiers.
Literature: xe2x80x9cKosmetikxe2x80x94Entwicklung, Herstellung und Anwendung kosmetischer Mittelxe2x80x9d [Cosmeticsxe2x80x94development, preparation and use of cosmetic agents]; W. Umbach (Editor), Georg Thieme Verlag 1988.
The temperature range in which the emulsifiers change their solubility is called the phase inversion temperature range. Within this specification, the abbreviation xe2x80x9cPITxe2x80x9d will also be used for the phase inversion temperature range.
As is known, the change in these solubility properties manifests itself in that a mixture of water, oil and O/W emulsifiers which gives an O/W emulsion after stirring below the PIT when brought to a temperature above the PIT, typically about 70-90xc2x0 C., can pass through the state of a microemulsion as an intermediate stage, to finally give a W/O emulsion above the PIT. If this emulsion is cooled, an O/W emulsion is obtained again, but this has a droplet size of up to 200 nm, and is in the region here between a microemulsion and a fine macroemulsion.
However, microemulsions of the prior art prepared in such a manner have the disadvantage that firstly the droplet size is still quite high, and that the emulsion is opaque white to bluish at room temperature and/or a high proportion of one or more emulsifiers is still necessary.
Another disadvantage is that although microemulsions prepared in such a manner are practically transparent at a high temperature, that is to say, for example, in the PIT, they become non-transparent again on falling to room temperature. Gels based on such microemulsions are thus at best unattractive, but also have disadvantages from the technical, galenical and cosmetic point of view.
The object was therefore also to remedy this poor state of affairs.
Astonishingly, all the objects on which the invention is based are achieved by microemulsion gels,
(a) based on microemulsions of the oil-in-water type, which comprise
an oily phase, which is essentially composed of constituents of low volatility, and an aqueous phase
comprising: one or more polyethoxylated O/W emulsifiers and/or one or more polypropoxylated O/W emulsifiers and/or one or more polyethoxylated and polypropoxylated O/W emulsifiers,
if desired furthermore comprising one or more W/O emulsifiers
having an emulsifier content of less than 20% by weight, based on the total weight of the emulsion,
obtainable by bringing a mixture of the base components, comprising the aqueous phase, the oily phase, one or more of the O/W emulsifiers according to the invention, if desired one or more W/O emulsifiers, and if desired further auxiliaries, additives and/or active compounds, to a temperature within or above the phase inversion temperature range, and thereafter cooling it to room temperature;
(b) in which the droplets of the discontinuous oily phase are joined to one another by one or more crosslinking substances, the molecules of which are distinguished by at least one hydrophilic region, which has an extension which is capable of bridging the distance between the microemulsion droplets, and by at least one hydrophobic region, which is capable of entering into a hydrophobic interaction with the microemulsion droplets.